The invention relates to a method and to a device for determining the position of an object within a given area, in particular, the position of the head of the front seat passenger in a vehicle.
In the last few years, airbag systems for reducing injuries in the case of accidents in motor vehicles have become widespread and have generally proven their value. As airbags have become increasingly common, individual cases have become known in which the airbag has led to an injury, in particular to a person located on the front passenger seat. The reason for this is usually that the airbag system does not have any reliable information on the position of the front seat passenger. The inflation process of the airbag is configured for extreme situations, i.e. an adult person wearing a seatbelt must not impact against the dashboard in the case of an accident. However, if the head of the front seat passenger is too close to the dashboard (out-of-position) at the time of inflation, this configuration of the airbag system can lead to serious injuries. There are numerous systems in development that are intended to remedy this problem. For example, attempts are being made to use laser triangulation sensors, if appropriate using ultrasound, to measure average distances in the respective vehicle passenger compartment under investigation, and to determine the position of the front seat passenger or of the head of the passenger therefrom. A difficulty here is that the head of the front seat passenger cannot be reliably distinguished from other objects.
Non-pre-published German patent application 198 09 210.5 discloses a method with which the described problem is to be remedied. In this method, the front seat passenger""s space is illuminated with a light source and the illuminated given area is recorded with a frame-producing video camera. The illumination is provided with a light beam composed of individual light rays that are bundled closely to one another so that a two-dimensional frame formed of dots is produced. The position of the front seat passenger is determined from the respective recorded two-dimensional dotted frame by determining the distances between the dots of the current dotted frame and the corresponding dots of an originally recorded, stored reference frame. The abovementioned method is relatively costly to execute because the generation of the light beam is costly. Furthermore, in particular, in frames with weak contrasts, it is difficult to make an assignment between a point, for example of the head of the front seat passenger, and the associated frame dots.
It is accordingly an object of the invention to provide a method and a device for determining the position of a moveable object which overcomes the above-mentioned disadvantages of the prior art apparatus and methods of this general type. In particular, it is an object of the invention to provide a method and a device for determining the position of a front seat passenger, who changes position, in a precise and easily executable manner.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for determining the position of a moveable object within a given area. The method includes steps of: taking a sequence of frames of a given area with a video camera and calculating a current position of an object in the given area by electronically evaluating the frames of the sequence; comparing a currently taken one of the frames with a previously stored one of the frames to produce a differential image in which a contour of the object appears only when the object moves; and calculating the position of the object based on the differential image.
A differential image is generated in which the contour of the object whose position is to be determined appears only when the object moves. In this way, in a given area, only the moving objects are automatically registered, which considerably simplifies the evaluation of the frames and at the same time makes it more reliable.
In accordance with an added mode of the invention, the object is a head of a front seat passenger in a vehicle.
In accordance with an additional mode of the invention, as long as the object is located within a predetermined region, the method includes: a1) calculating a current differential image; b1) extracting a current contour of the object from the current differential image; c1) after initiation, defining a first contour and using the first contour as a template; for all further contours, incorporating the current contour into the template in a weighted manner; and d1) repetitively performing steps a1 through c1 in order.
In accordance with another mode of the invention, if the object moves out of the predetermined region, the method includes: a2) calculating the current differential image; b2) extracting the current contour from the current differential image; c2) calculating the position of the object using a cross-correlation of the current contour with the template; d2) if a magnitude of the correlation exceeds a predefined amount, centering a measuring window on the current contour, replacing the template with the current contour, and going to step e2); in an absence of a differential image, jumping to step a2); otherwise jumping to step a1); e2) if the contour is again within the predetermined region: jumping to step a1); f2) if the contour moves in a predetermined warning region, issuing an alarm signal; and h2) jumping to step a2).
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for determining the position of a moveable object within a given area, that includes: a video camera with a defined frame sequence time; a control unit with a computer unit; and a frame storage device storing evaluation software; the evaluation software configured to perform the method described above.
In accordance with an added feature of the invention, the frame storage device has a capacity for storing at least five frames.
In accordance with an additional feature of the invention, the video camera is either a CCD camera or a CMOS camera.
In accordance with another feature of the invention, the object is a head of a passenger in a front seat of a vehicle having a dashboard; the video camera has an optical axis and is configured such that the optical axis is aligned approximately perpendicularly with respect to a plane in which movements of the passenger normally take place between the front seat and the dashboard; and the camera has optics that register at least approximately in the region between the passenger and the dashboard.
In accordance with a further feature of the invention, an airbag control device is provided that is activated dependent on a prediction of when the head of the passenger will penetrate into a hazard range. The prediction is based on the trajectory of the head and the speed of the head.
In accordance with a further added feature of the invention, an infrared light source is provided, and the video camera is provided with a filter that cuts out wavelengths below a near infrared spectrum range.
In accordance with yet another feature of the invention, the control device receives an emergency braking signal when an emergency braking occurs.
The device does not necessarily need to operate with an extraneous light source, but can instead use daylight, for example, depending on the purpose of use.
The determination of the position of the object is carried out merely by evaluating successively recorded frames using a suitable evaluation software. There is no need for a complicated light source.
An advantage of the invention lies in particular in the robustness of the evaluation method which supplies reliable results.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a method and device for determining the position of an object within a given area, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.